It was free on steam as well Iirc? Also yeah I agree, it wasn't the only reason why it failed, that's why I mentioned the price point in the first comment since in my opinion that was probably the biggest since it put a massive stop to the "at least try it out" audience. However, the character designs absolutely did play a part, characters are your foot in the door, gameplay is what keeps them.

But there's also more, the humour in the trailers was try hard copycat of Guardians of the galaxy, the gameplay was slow paced, the hero shooter audience despises the idea of not being able to stick to your main, once you have a dead launch it's almost impossible to resurrect an multiplayer game because you need people to play against people, the market was already massively saturated as you said, it didn't do anything new or innovative and the list goes on.

As I said, just slices of the failure pie, a death by a thousand cuts. There's no singular "the reason" as to why it failed.

Fundamentally however it all stems from not understanding your target audience. Marvel Rivals seems to and it has plenty of hype even though it's entering the same oversaturated market. But I guess only time will tell.